1. Field of Invention
The present invention relates generally to a dust tolerant windowless scanner and, more specifically, to a dust tolerant windowless scanner and its media scan assembly.
2. Description of the Related Art
Scanners typically include an array of optical sensor elements and a scan area (e.g., plate of glass) where an object to be imaged by the sensor elements is positioned. An optical path including, for example, lenses and mirrors, spans between the sensor elements and the scan area.
Referring to FIG. 3, a conventional scanner 300 includes a main housing 302, a glass plate 304, mirrors 306, 308, 310 and a lens 312 configured as shown. An optical path 314 of the scanner 300 begins at an object focal plane 316 at the top surface of the glass plate 304, reflects from the mirrors 306, 308, 310 as shown, and passes through the lens 312 to end at the sensor focal plane 318 (shown with a dashed line).
The scanner 300, as well as other conventional sheet fed facsimile and All-in-One products, employs the glass plate 304 for the object being scanned to reference against while the object is in the scan zone. The object to be scanned is moved over the object focal plane 316 by employing, for example, a conventional automatic document feeder (not shown).
A problem with the conventional scanner 300 is that the glass plate 304 must be positioned at or very near the object focal plane 316 in order for the glass plate 304 to fulfill its intended purpose of document support. Unfortunately, the positioning of the glass plate 304 in this manner provides locations (on both sides of the glass plate 304) very near the object focal plane 316 for dust or debris to accumulate. The scanner 300 is therefore highly sensitive to any small piece of dust or debris, resulting in streaks (typically, vertical streaks) on the scanned image in the direction of paper motion. Moreover, dust or debris on the reflecting surface of the mirror 306 may also be imaged due to its close proximity (e.g., 15 mm) to the object focal plane 316. The term “dust or debris” means optical obstructions which may effect the transmission of light and includes, but is not limited to, paper dust, plastic dust, skin particles, metal particles, glass particles and fibers.
Although dust or debris on the top surface of the glass plate 304 can be easily removed, it is difficult to clean dust or debris from the inside of the scanner 300 particularly after the scanner 300 has been assembled. As a result, the scanner 300 is typically built on a “clean line” to lessen the number of product returns. This, of course, increases the manufacturing cost of the conventional scanner 300. Thus, a need exists for a low cost dust tolerant scanner which is less sensitive to particle contamination.